the background. This issue (pair) came in sheets of 50 (100 individual stamps), with an initial printing of 150 million. Skylab Issue of 1974 Skylab, a science and engineering laboratory, was the United States' first space station, and the second space station visited by a human crew. It was put into orbit by a Saturn V rocket on 14 May 1973. It was also the only space station NASA launched alone. The 100-ton space station was in Earth's orbit from 1973 to 1979 and it was visited by crews three times in 1973 and 1974. Circling 50 degrees north and south of the equator at an altitude of , Skylab had an orbital period of 93 minutes. There were a plethora of UV astronomy experiments done during the Skylab lifetime, as well as detailed X-ray studies of the Sun. The station was active until July 11, 1979, when it fell out of orbit. The 10-cent Skylab commemorative stamp first day of release took place at Houston, Texas, on May 14, 1974. This issue commemorates the first anniversary of the launching of Skylab, and depicts the station as it was repaired, complete with "umbrella" and missing the lost solar panel. The stamp was designed by Robert T. McCall and was issued in sheets of fifty, with an initial printing of 140 million. Pioneer Commemorative Issue of 1975 In March 1972, scientists at NASA launched Pioneer 10 to gather scientific data about the Solar System's largest planet, Jupiter, while the vessel was also receiving radio control and guidance signals and other information from Earth. Pioneer 10 was expected to last for 21 months in the Solar System and deliver accurate information over that period of time. The fastest man made object to enter space from Earth, the spacecraft was to begin collecting data at the Asteroid Belt and Jupiter and continue to relay information about other areas and phenomena of the Solar System. After Pioneer 10 passed through the asteroid belt, Pioneer 11, was launched on a similar trajectory. Pioneer 10 became the first spacecraft to get close enough to Jupiter to send back revelations about the properties and phenomena of the Solar System's largest planet. The 10-cent Pioneer commemorative stamp was issued on February 28, 1975, at Mountain View, California, and paid the domestic first-class rate for letters weighing less than one half ounce. Designed by Robert T. McCall and printed